The objective of the proposed research is to define the mechanism of interaction of activated electrophilic metabolites of carcinogenic nitrosamines with cellular targets such as nucleophilic sites on the DNA molecule. The hypothesis that alklylation of nucleic acids proceeds by a unimolecular nucleophilic substitution (SNI) reaction is being investigated. Di-n-propyl-nitrosamine will be administered to rats followed by isolation of DNA and RNA from the livers. If the alkylation proceeds via an SNI mechanism, 7-isopropylguanine should be the major propylated base isolated together with small amounts of 7-n-propylguanine. If a biomolecular nucleophilic substitution reaction is operative, only n-propylguanine will be isolated. The ratio of propylated isomers following incubation of di-n-propylnitrosamine in vitro with isolated microsomes in the presence of guanine and calf thymus DNA will also be investigated.